Blueshift, in a motorcycle engine (or a outboard motor engine, or a snowmobile engine or most any other small gasoline engine), the intake plenum volume between the carb and the valve is pretty small, maybe 1-2 stroke displacements or less, therefore the control hysteresis (acelleration lag, and decelleration overshoot) is going to be pretty small or non-existant for them compared to the plenum volume on a typical 4 or 6 cylinder auto engine. but you are right, the PRIMARY focus is emissions control with cost being a close second. And as a previous poster stated, multiple jets/venturi are required usually with some complex mechanical controls to compensate for the airflow changes between idle and full throttle and for outside air temp. and even humidity can be compensated for with electronic injection controls unlike the mechanical carb controls. Things that can be compensated for electronically much easier and cheaper (and better!) than the mechanical linkages required for a similar control scheme.